The communications controllers are data processing equipment designed to be incorporated into data teleprocessing network so as to handle transmissions over various lines which are connected thereto. Generally, the main control of the data tele-processing network is concentrated into one or several central processing units having a list of the data processing rules for processing the data coming from/or to be sent to terminal stations, or terminals, of the data tele-processing network. Both transmission and reception of the data through the communications lines, are processed by communications controllers controlled by the central processing unit(s) (CPU's). Besides the processing functions, the controller is in charge of carrying out directory functions, more specifically, functions directly relevant to the standard transmission procedures. Consequently, the central processing units (CPU's) are released from the corresponding tasks and can devote itself to carrying out other operations.
The communications controller is a complex assembly the intelligence of which is most concentrated in one or several central control units CCU's. The central control units are connected to the terminals through line adapters and to the central processing units CPU's through channel adapters which are so designated since they are connected to the channels of the central processing unit(s).
The line adapters can serve a number of communications lines by means of a cyclical scanning device comprised of an assembly of random access memories wherein the data are buffered, which are received from the various lines or which must be transmitted thereto, under the control of the scanning device. The line adapters have, each, a microprocessor which releases the central control units from a number of tasks, such as handling the data exchanged between the central control unit CCU and the lines, on both transmission and reception sides.
In such an environment, it is necessary for the error conditions detected in a line adapter, to be reported to the central control unit. Various approachs can be contemplated to perform this function. For instance, only the microcode of the microprocessor could be used. Such an approach has for a drawback that, when the error condition has entailed a failure in the microprocessor, the microcode integrity may not be insured and, as a consequence, the error conditions are not reported to the central control unit by the microcode.
Another approach would consist in providing each line adapter with two microprocessors. It is obvious that such an approach is expensive for both hardware and software points of view because it requires means for handling the exchanges between the two microprocessors.
A third approach would consist in dedicating a special path for error reporting. Such an approach is also expensive because it requires additional hardware and additional programming development to support this new path.
An object of this invention is to provide each adapter with a device for reporting the error conditions occurring in the line adapters, to the central processing unit without assistance from microcode-controlled microprocessors handling the data exchanged between the lines connected to the adapters and the central control unit, when the microcode integrity is affected by error conditions.